This invention relates to an articulated robot mechanism used for assembling and working (machining) operations, and more particularly to a six-degree-of-freedom articulated robot mechanism capable of effecting highly-precise positioning and orienting and also of effecting highly-precise assembling and working operations. The invention also relates to an assembling and working apparatus employing such a robot mechanism.
Generally, there are three degrees of freedom of the position of an object, and there are three degrees of freedom of its orientation. Therefore, a robot capable of providing any desired position and orientation is required to have six degrees of freedom. There are four methods of providing three degrees of freedom of the position. These four methods are, respectively, a Cartesian coordinates-type depending on three translational motions, a cylindrical coordinates-type depending on two translational motions and one rotation, a polar coordinates-type depending on one translational motion and two rotations, and an articulation-type depending on three rotations. With respect to a method of providing three degrees of freedom of the orientation, the three motions must all depend on rotations.
Under the circumstances, there has been proposed a six-degree-of-freedom robot of the type, as disclosed in Japanese Patent Unexamined Publication No. 60-52276, which comprises a four-degree-of-freedom unit having three degrees of freedom of the position in polar coordinates and one degree of freedom of the orientation, and a two-degree-of-freedom unit having two degrees of freedom of the orientation.
In the above prior art, five out of six degrees of freedom are effected by rotation articulation mechanisms each in the form of a rotation transmission mechanism comprising a servo motor and a reduction gear unit, or a servo motor, a belt and pulleys. The remaining one degree of freedom is effected by a translation transmission mechanism comprising a servo motor and a feed screw. Thus, in any of these mechanisms, the drive motor is not directly connected to an arm or a table, and therefore there has been encountered a problem that due to play and lost motion occurring in the reduction gear portion contained in the rotation transmission mechanism or the translation transmission mechanism, the positioning precision of the robot is lowered.
As described above, the above prior art has not paid attention to the compatibility between the flexibility and high-precision positioning of the robot, and therefore has a problem with respect to a high-function and high-performance design of the robot.
Referring to the conventional operation apparatus of the automatic tool exchanging type for automatically exchanging a plurality of tools so as to effect various operations such as assembling and adjusting operations, Japanese Patent Unexamined Publication No. 63-39780 discloses an automatic tool exchange apparatus employing a robot hand, and Japanese Patent Unexamined Publication No. 62-9887 discloses an automatic hand exchange apparatus, and Japanese Patent Unexamined Publication No. 61-117087 discloses an attachment/detachment apparatus. In such apparatuses, the tools are exchanged depending on the purpose of the operation, and various operations such as assembling and adjusting operations can be carried out.
In the conventional tool exchange apparatuses, a drive actuator must be mounted on each hand or each tool (end effector), so that the end effector has an increased size, and the costs of the exchange end effectors and the exchange tools have been increased. In addition, the burden on the exchange apparatus has been increased. Further, since each end effector has an increased size, a large space for accommodating the end effectors has been needed.
Further, since the actuator is mounted on the end effector, signal wires and a power cable for the actuator can not be easily treated, and also in the case where the signal wires and power cable for the actuator are connected through contact terminals, the available terminals are mostly occupied by these contact terminals, so that the number of those terminals other than the contact terminals is reduced, and also the contact terminal portion has been increased in size.
Further, no consideration has been given to the change of the freedom degree by the addition of an effector (for example, a robot arm) other than those for the hands and the tools. Thus, this problem has not been dealt with.